Big profiles, a little faster again

One more round of work on profiles with very large game libraries. - To work out your base-game completion rate and Mythic progress, CompletionLab checks which achievements belong to each game's Base Game. That check now reads your library with less work per achievement, and no longer looks up the same saved result twice. - For the largest library on CompletionLab, the profile now loads in about 3.7 seconds instead of about 4.3, and its share card in about 3 seconds instead of 3.5. - Smaller profiles are unchanged or slightly quicker. - The rules haven't changed, and every number stays exactly the same: Gamerscore, completion, Mythics, Prestige and your base-game rate.